1. Field of the Invention
This invention relates to a lightning arrester monitor which is used for assessing any degradation of a zinc-oxide-type element used in a lightning arrester.
2. Description of the Related Art
FIG. 1 schematically shows, by way of example, the construction of a conventional automatic lightning arrester monitor which is disclosed in Japanese Patent Laid-Open No. 61-203586. As shown in the drawing, an instrument box 3 which is grounded by means of a grounding cable 2 is provided for a lightning arrester 1 equipped with a zinc-oxide-type element. Arranged in this instrument box 3 are a current transformer 4 for measuring leakage current and a shielded cable 5 for transmitting a signal from this current transformer 4 to a signal processing circuit (not shown).
The operation of the above conventional lightning arrester monitor will now be described. A very small amount of leakage current normally flows through the grounding cable 2 of the lightning arrester 1. This leakage current exhibits a constant value except during the operation of the lightning arrester 1. By monitoring to see whether or not the leakage current exhibits a constant value, it can be ascertained whether or not the lightning arrester is in the normal condition. The current transformer 4, which is provided in the grounded instrument box 3 for the purpose of measuring leakage current, generates an electric signal, which is transmitted to a signal processing circuit (not shown) through the shielded cable 5. The monitoring of the lightning arrester 1 is conducted on the basis of any changes in this electric signal.
A problem in the above-described conventional lightning arrester monitor is that a complicated electric circuit providing high accuracy is needed for detecting leakage current.